[PATCH net-next v4 0/6] net: qualcomm: rmnet: stop using C bit-fields

[PATCH net-next v4 0/6] net: qualcomm: rmnet: stop using C bit-fields

[Alex Elder]

The main reason for version 4 of this series is that a bug was
introduced in version 3, and that is fixed.

But a nice note from Vladimir Oltean got me thinking about the
necessity of using accessors defined in <linux/bitfield.h>, and I
concluded there was no need.  So this version simplifies things
further, using bitwise AND and OR operators (rather than, e.g.,
u8_get_bits()) to access all values encoded in bit fields.

This version has been tested using IPv4 with checksum offload
enabled and disabled.  Traffic over the link included ICMP (ping),
UDP (iperf), and TCP (wget).

Version 3 of this series used BIT() rather than GENMASK() to define
single-bit masks, and bitwise AND operators to access them.

Version 2 fixed bugs in the way the value written into the header
was computed in version 1.

The series was first posted here:
  https://lore.kernel.org/netdev/20210304223431.15045-1-elder@linaro.org/

					-Alex

Alex Elder (6):
  net: qualcomm: rmnet: mark trailer field endianness
  net: qualcomm: rmnet: simplify some byte order logic
  net: qualcomm: rmnet: kill RMNET_MAP_GET_*() accessor macros
  net: qualcomm: rmnet: use masks instead of C bit-fields
  net: qualcomm: rmnet: don't use C bit-fields in rmnet checksum trailer
  net: qualcomm: rmnet: don't use C bit-fields in rmnet checksum header

 .../ethernet/qualcomm/rmnet/rmnet_handlers.c  | 10 +--
 .../net/ethernet/qualcomm/rmnet/rmnet_map.h   | 12 ----
 .../qualcomm/rmnet/rmnet_map_command.c        | 11 +++-
 .../ethernet/qualcomm/rmnet/rmnet_map_data.c  | 60 ++++++++---------
 include/linux/if_rmnet.h                      | 65 +++++++++----------
 5 files changed, 69 insertions(+), 89 deletions(-)

-- 
2.27.0

[PATCH net-next v4 1/6] net: qualcomm: rmnet: mark trailer field endianness

[Alex Elder]

The fields in the checksum trailer structure used for QMAP protocol
RX packets are all big-endian format, so define them that way.

It turns out these fields are never actually used by the RMNet code.
The start offset is always assumed to be zero, and the length is
taken from the other packet headers.  So making these fields
explicitly big endian has no effect on the behavior of the code.

Signed-off-by: Alex Elder <elder@linaro.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
---
 include/linux/if_rmnet.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/if_rmnet.h b/include/linux/if_rmnet.h
index 9661416a9bb47..8c7845baf3837 100644
--- a/include/linux/if_rmnet.h
+++ b/include/linux/if_rmnet.h
@@ -32,8 +32,8 @@ struct rmnet_map_dl_csum_trailer {
 #else
 #error	"Please fix <asm/byteorder.h>"
 #endif
-	u16 csum_start_offset;
-	u16 csum_length;
+	__be16 csum_start_offset;
+	__be16 csum_length;
 	__be16 csum_value;
 } __aligned(1);
 
-- 
2.27.0

[PATCH net-next v4 2/6] net: qualcomm: rmnet: simplify some byte order logic

[Alex Elder]

In rmnet_map_ipv4_ul_csum_header() and rmnet_map_ipv6_ul_csum_header()
the offset within a packet at which checksumming should commence is
calculated.  This calculation involves byte swapping and a forced type
conversion that makes it hard to understand.

Simplify this by computing the offset in host byte order, then
converting the result when assigning it into the header field.

Signed-off-by: Alex Elder <elder@linaro.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
---
 .../ethernet/qualcomm/rmnet/rmnet_map_data.c  | 22 ++++++++++---------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
index 21d38167f9618..bd1aa11c9ce59 100644
--- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
+++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
@@ -197,12 +197,13 @@ rmnet_map_ipv4_ul_csum_header(void *iphdr,
 			      struct rmnet_map_ul_csum_header *ul_header,
 			      struct sk_buff *skb)
 {
-	struct iphdr *ip4h = (struct iphdr *)iphdr;
-	__be16 *hdr = (__be16 *)ul_header, offset;
+	__be16 *hdr = (__be16 *)ul_header;
+	struct iphdr *ip4h = iphdr;
+	u16 offset;
+
+	offset = skb_transport_header(skb) - (unsigned char *)iphdr;
+	ul_header->csum_start_offset = htons(offset);
 
-	offset = htons((__force u16)(skb_transport_header(skb) -
-				     (unsigned char *)iphdr));
-	ul_header->csum_start_offset = offset;
 	ul_header->csum_insert_offset = skb->csum_offset;
 	ul_header->csum_enabled = 1;
 	if (ip4h->protocol == IPPROTO_UDP)
@@ -239,12 +240,13 @@ rmnet_map_ipv6_ul_csum_header(void *ip6hdr,
 			      struct rmnet_map_ul_csum_header *ul_header,
 			      struct sk_buff *skb)
 {
-	struct ipv6hdr *ip6h = (struct ipv6hdr *)ip6hdr;
-	__be16 *hdr = (__be16 *)ul_header, offset;
+	__be16 *hdr = (__be16 *)ul_header;
+	struct ipv6hdr *ip6h = ip6hdr;
+	u16 offset;
+
+	offset = skb_transport_header(skb) - (unsigned char *)ip6hdr;
+	ul_header->csum_start_offset = htons(offset);
 
-	offset = htons((__force u16)(skb_transport_header(skb) -
-				     (unsigned char *)ip6hdr));
-	ul_header->csum_start_offset = offset;
 	ul_header->csum_insert_offset = skb->csum_offset;
 	ul_header->csum_enabled = 1;
 
-- 
2.27.0

Re: [PATCH net-next v4 2/6] net: qualcomm: rmnet: simplify some byte order logic

[Alexander Duyck]

On Mon, Mar 15, 2021 at 6:36 AM Alex Elder <elder@linaro.org> wrote:
>
> In rmnet_map_ipv4_ul_csum_header() and rmnet_map_ipv6_ul_csum_header()
> the offset within a packet at which checksumming should commence is
> calculated.  This calculation involves byte swapping and a forced type
> conversion that makes it hard to understand.
>
> Simplify this by computing the offset in host byte order, then
> converting the result when assigning it into the header field.
>
> Signed-off-by: Alex Elder <elder@linaro.org>
> Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
> ---
>  .../ethernet/qualcomm/rmnet/rmnet_map_data.c  | 22 ++++++++++---------
>  1 file changed, 12 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> index 21d38167f9618..bd1aa11c9ce59 100644
> --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
> @@ -197,12 +197,13 @@ rmnet_map_ipv4_ul_csum_header(void *iphdr,
>                               struct rmnet_map_ul_csum_header *ul_header,
>                               struct sk_buff *skb)
>  {
> -       struct iphdr *ip4h = (struct iphdr *)iphdr;
> -       __be16 *hdr = (__be16 *)ul_header, offset;
> +       __be16 *hdr = (__be16 *)ul_header;
> +       struct iphdr *ip4h = iphdr;
> +       u16 offset;
> +
> +       offset = skb_transport_header(skb) - (unsigned char *)iphdr;
> +       ul_header->csum_start_offset = htons(offset);

Rather than using skb_transport_header the correct pointer to use is
probably skb_checksum_start. The two are essentially synonymous but
the checksumming code is supposed to use skb_checksum_start.

Alternatively you could look at possibly using skb_network_header_len
as that would be the same value assuming that both headers are the
outer headers. Then you could avoid the extra pointer overhead.

>
> -       offset = htons((__force u16)(skb_transport_header(skb) -
> -                                    (unsigned char *)iphdr));
> -       ul_header->csum_start_offset = offset;
>         ul_header->csum_insert_offset = skb->csum_offset;
>         ul_header->csum_enabled = 1;
>         if (ip4h->protocol == IPPROTO_UDP)
> @@ -239,12 +240,13 @@ rmnet_map_ipv6_ul_csum_header(void *ip6hdr,
>                               struct rmnet_map_ul_csum_header *ul_header,
>                               struct sk_buff *skb)
>  {
> -       struct ipv6hdr *ip6h = (struct ipv6hdr *)ip6hdr;
> -       __be16 *hdr = (__be16 *)ul_header, offset;
> +       __be16 *hdr = (__be16 *)ul_header;
> +       struct ipv6hdr *ip6h = ip6hdr;
> +       u16 offset;
> +
> +       offset = skb_transport_header(skb) - (unsigned char *)ip6hdr;
> +       ul_header->csum_start_offset = htons(offset);

Same here.

>
> -       offset = htons((__force u16)(skb_transport_header(skb) -
> -                                    (unsigned char *)ip6hdr));
> -       ul_header->csum_start_offset = offset;
>         ul_header->csum_insert_offset = skb->csum_offset;
>         ul_header->csum_enabled = 1;
>
> --
> 2.27.0
>

Re: [PATCH net-next v4 2/6] net: qualcomm: rmnet: simplify some byte order logic

[Alex Elder]

On 3/15/21 11:02 AM, Alexander Duyck wrote:
> On Mon, Mar 15, 2021 at 6:36 AM Alex Elder <elder@linaro.org> wrote:
>>
>> In rmnet_map_ipv4_ul_csum_header() and rmnet_map_ipv6_ul_csum_header()
>> the offset within a packet at which checksumming should commence is
>> calculated.  This calculation involves byte swapping and a forced type
>> conversion that makes it hard to understand.
>>
>> Simplify this by computing the offset in host byte order, then
>> converting the result when assigning it into the header field.
>>
>> Signed-off-by: Alex Elder <elder@linaro.org>
>> Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
>> ---
>>   .../ethernet/qualcomm/rmnet/rmnet_map_data.c  | 22 ++++++++++---------
>>   1 file changed, 12 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
>> index 21d38167f9618..bd1aa11c9ce59 100644
>> --- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
>> +++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
>> @@ -197,12 +197,13 @@ rmnet_map_ipv4_ul_csum_header(void *iphdr,
>>                                struct rmnet_map_ul_csum_header *ul_header,
>>                                struct sk_buff *skb)
>>   {
>> -       struct iphdr *ip4h = (struct iphdr *)iphdr;
>> -       __be16 *hdr = (__be16 *)ul_header, offset;
>> +       __be16 *hdr = (__be16 *)ul_header;
>> +       struct iphdr *ip4h = iphdr;
>> +       u16 offset;
>> +
>> +       offset = skb_transport_header(skb) - (unsigned char *)iphdr;
>> +       ul_header->csum_start_offset = htons(offset);
> 
> Rather than using skb_transport_header the correct pointer to use is
> probably skb_checksum_start. The two are essentially synonymous but
> the checksumming code is supposed to use skb_checksum_start.

That's a great suggestion.  I was mimicking the existing
code but it would be much better to use that.

> Alternatively you could look at possibly using skb_network_header_len
> as that would be the same value assuming that both headers are the
> outer headers. Then you could avoid the extra pointer overhead.

Actually, I think this is better still, because the purpose
here is to tell the hardware where to start checksumming.
I.e., it's unrelated to the SKB, and hides the calculation.

Thank you.  I'll put together version 5, incorporating your
suggestion.

					-Alex

>> -       offset = htons((__force u16)(skb_transport_header(skb) -
>> -                                    (unsigned char *)iphdr));
>> -       ul_header->csum_start_offset = offset;
>>          ul_header->csum_insert_offset = skb->csum_offset;
>>          ul_header->csum_enabled = 1;
>>          if (ip4h->protocol == IPPROTO_UDP)
>> @@ -239,12 +240,13 @@ rmnet_map_ipv6_ul_csum_header(void *ip6hdr,
>>                                struct rmnet_map_ul_csum_header *ul_header,
>>                                struct sk_buff *skb)
>>   {
>> -       struct ipv6hdr *ip6h = (struct ipv6hdr *)ip6hdr;
>> -       __be16 *hdr = (__be16 *)ul_header, offset;
>> +       __be16 *hdr = (__be16 *)ul_header;
>> +       struct ipv6hdr *ip6h = ip6hdr;
>> +       u16 offset;
>> +
>> +       offset = skb_transport_header(skb) - (unsigned char *)ip6hdr;
>> +       ul_header->csum_start_offset = htons(offset);
> 
> Same here.
> 
>>
>> -       offset = htons((__force u16)(skb_transport_header(skb) -
>> -                                    (unsigned char *)ip6hdr));
>> -       ul_header->csum_start_offset = offset;
>>          ul_header->csum_insert_offset = skb->csum_offset;
>>          ul_header->csum_enabled = 1;
>>
>> --
>> 2.27.0
>>

[PATCH net-next v4 3/6] net: qualcomm: rmnet: kill RMNET_MAP_GET_*() accessor macros

[Alex Elder]

The following macros, defined in "rmnet_map.h", assume a socket
buffer is provided as an argument without any real indication this
is the case.
    RMNET_MAP_GET_MUX_ID()
    RMNET_MAP_GET_CD_BIT()
    RMNET_MAP_GET_PAD()
    RMNET_MAP_GET_CMD_START()
    RMNET_MAP_GET_LENGTH()
What they hide is pretty trivial accessing of fields in a structure,
and it's much clearer to see this if we do these accesses directly.

So rather than using these accessor macros, assign a local
variable of the map header pointer type to the socket buffer data
pointer, and derereference that pointer variable.

In "rmnet_map_data.c", use sizeof(object) rather than sizeof(type)
in one spot.  Also, there's no need to byte swap 0; it's all zeros
irrespective of endianness.

Signed-off-by: Alex Elder <elder@linaro.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
---
 drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c | 10 ++++++----
 drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h      | 12 ------------
 .../net/ethernet/qualcomm/rmnet/rmnet_map_command.c  | 11 ++++++++---
 drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c |  4 ++--
 4 files changed, 16 insertions(+), 21 deletions(-)

diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
index 3d00b32323084..2a6b2a609884c 100644
--- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
+++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
@@ -56,20 +56,22 @@ static void
 __rmnet_map_ingress_handler(struct sk_buff *skb,
 			    struct rmnet_port *port)
 {
+	struct rmnet_map_header *map_header = (void *)skb->data;
 	struct rmnet_endpoint *ep;
 	u16 len, pad;
 	u8 mux_id;
 
-	if (RMNET_MAP_GET_CD_BIT(skb)) {
+	if (map_header->cd_bit) {
+		/* Packet contains a MAP command (not data) */
 		if (port->data_format & RMNET_FLAGS_INGRESS_MAP_COMMANDS)
 			return rmnet_map_command(skb, port);
 
 		goto free_skb;
 	}
 
-	mux_id = RMNET_MAP_GET_MUX_ID(skb);
-	pad = RMNET_MAP_GET_PAD(skb);
-	len = RMNET_MAP_GET_LENGTH(skb) - pad;
+	mux_id = map_header->mux_id;
+	pad = map_header->pad_len;
+	len = ntohs(map_header->pkt_len) - pad;
 
 	if (mux_id >= RMNET_MAX_LOGICAL_EP)
 		goto free_skb;
diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h
index 576501db2a0bc..2aea153f42473 100644
--- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h
+++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map.h
@@ -32,18 +32,6 @@ enum rmnet_map_commands {
 	RMNET_MAP_COMMAND_ENUM_LENGTH
 };
 
-#define RMNET_MAP_GET_MUX_ID(Y) (((struct rmnet_map_header *) \
-				 (Y)->data)->mux_id)
-#define RMNET_MAP_GET_CD_BIT(Y) (((struct rmnet_map_header *) \
-				(Y)->data)->cd_bit)
-#define RMNET_MAP_GET_PAD(Y) (((struct rmnet_map_header *) \
-				(Y)->data)->pad_len)
-#define RMNET_MAP_GET_CMD_START(Y) ((struct rmnet_map_control_command *) \
-				    ((Y)->data + \
-				      sizeof(struct rmnet_map_header)))
-#define RMNET_MAP_GET_LENGTH(Y) (ntohs(((struct rmnet_map_header *) \
-					(Y)->data)->pkt_len))
-
 #define RMNET_MAP_COMMAND_REQUEST     0
 #define RMNET_MAP_COMMAND_ACK         1
 #define RMNET_MAP_COMMAND_UNSUPPORTED 2
diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_command.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_command.c
index beaee49621287..add0f5ade2e61 100644
--- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_command.c
+++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_command.c
@@ -12,12 +12,13 @@ static u8 rmnet_map_do_flow_control(struct sk_buff *skb,
 				    struct rmnet_port *port,
 				    int enable)
 {
+	struct rmnet_map_header *map_header = (void *)skb->data;
 	struct rmnet_endpoint *ep;
 	struct net_device *vnd;
 	u8 mux_id;
 	int r;
 
-	mux_id = RMNET_MAP_GET_MUX_ID(skb);
+	mux_id = map_header->mux_id;
 
 	if (mux_id >= RMNET_MAX_LOGICAL_EP) {
 		kfree_skb(skb);
@@ -49,6 +50,7 @@ static void rmnet_map_send_ack(struct sk_buff *skb,
 			       unsigned char type,
 			       struct rmnet_port *port)
 {
+	struct rmnet_map_header *map_header = (void *)skb->data;
 	struct rmnet_map_control_command *cmd;
 	struct net_device *dev = skb->dev;
 
@@ -58,7 +60,8 @@ static void rmnet_map_send_ack(struct sk_buff *skb,
 
 	skb->protocol = htons(ETH_P_MAP);
 
-	cmd = RMNET_MAP_GET_CMD_START(skb);
+	/* Command data immediately follows the MAP header */
+	cmd = (struct rmnet_map_control_command *)(map_header + 1);
 	cmd->cmd_type = type & 0x03;
 
 	netif_tx_lock(dev);
@@ -71,11 +74,13 @@ static void rmnet_map_send_ack(struct sk_buff *skb,
  */
 void rmnet_map_command(struct sk_buff *skb, struct rmnet_port *port)
 {
+	struct rmnet_map_header *map_header = (void *)skb->data;
 	struct rmnet_map_control_command *cmd;
 	unsigned char command_name;
 	unsigned char rc = 0;
 
-	cmd = RMNET_MAP_GET_CMD_START(skb);
+	/* Command data immediately follows the MAP header */
+	cmd = (struct rmnet_map_control_command *)(map_header + 1);
 	command_name = cmd->command_name;
 
 	switch (command_name) {
diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
index bd1aa11c9ce59..fd55269c2ce3c 100644
--- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
+++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
@@ -321,7 +321,7 @@ struct sk_buff *rmnet_map_deaggregate(struct sk_buff *skb,
 		return NULL;
 
 	maph = (struct rmnet_map_header *)skb->data;
-	packet_len = ntohs(maph->pkt_len) + sizeof(struct rmnet_map_header);
+	packet_len = ntohs(maph->pkt_len) + sizeof(*maph);
 
 	if (port->data_format & RMNET_FLAGS_INGRESS_MAP_CKSUMV4)
 		packet_len += sizeof(struct rmnet_map_dl_csum_trailer);
@@ -330,7 +330,7 @@ struct sk_buff *rmnet_map_deaggregate(struct sk_buff *skb,
 		return NULL;
 
 	/* Some hardware can send us empty frames. Catch them */
-	if (ntohs(maph->pkt_len) == 0)
+	if (!maph->pkt_len)
 		return NULL;
 
 	skbn = alloc_skb(packet_len + RMNET_MAP_DEAGGR_SPACING, GFP_ATOMIC);
-- 
2.27.0

[PATCH net-next v4 4/6] net: qualcomm: rmnet: use masks instead of C bit-fields

[Alex Elder]

The actual layout of bits defined in C bit-fields (e.g. int foo : 3)
is implementation-defined.  Structures defined in <linux/if_rmnet.h>
address this by specifying all bit-fields twice, to cover two
possible layouts.

I think this pattern is repetitive and noisy, and I find the whole
notion of compiler "bitfield endianness" to be non-intuitive.

Stop using C bit-fields for the command/data flag and the pad length
fields in the rmnet_map structure, and define a single-byte flags
field instead.  Define a mask for the single bit "command" flag,
and another mask for the encoded pad length.  The content of both
fields can be accessed using a simple bitwise AND operation.

Signed-off-by: Alex Elder <elder@linaro.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
---
v4: - Don't use u8_get_bits() to access the pad length
    - Added BUILD_BUG_ON() to ensure field width is adequate
v3: - Use BIT(x) and don't use u8_get_bits() for the command flag

 .../ethernet/qualcomm/rmnet/rmnet_handlers.c  |  4 ++--
 .../ethernet/qualcomm/rmnet/rmnet_map_data.c  |  4 +++-
 include/linux/if_rmnet.h                      | 23 ++++++++-----------
 3 files changed, 15 insertions(+), 16 deletions(-)

diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
index 2a6b2a609884c..0be5ac7ab2617 100644
--- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
+++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_handlers.c
@@ -61,7 +61,7 @@ __rmnet_map_ingress_handler(struct sk_buff *skb,
 	u16 len, pad;
 	u8 mux_id;
 
-	if (map_header->cd_bit) {
+	if (map_header->flags & MAP_CMD_FLAG) {
 		/* Packet contains a MAP command (not data) */
 		if (port->data_format & RMNET_FLAGS_INGRESS_MAP_COMMANDS)
 			return rmnet_map_command(skb, port);
@@ -70,7 +70,7 @@ __rmnet_map_ingress_handler(struct sk_buff *skb,
 	}
 
 	mux_id = map_header->mux_id;
-	pad = map_header->pad_len;
+	pad = map_header->flags & MAP_PAD_LEN_MASK;
 	len = ntohs(map_header->pkt_len) - pad;
 
 	if (mux_id >= RMNET_MAX_LOGICAL_EP)
diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
index fd55269c2ce3c..3c3307949db00 100644
--- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
+++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
@@ -286,6 +286,7 @@ struct rmnet_map_header *rmnet_map_add_map_header(struct sk_buff *skb,
 		return map_header;
 	}
 
+	BUILD_BUG_ON(MAP_PAD_LEN_MASK < 3);
 	padding = ALIGN(map_datalen, 4) - map_datalen;
 
 	if (padding == 0)
@@ -299,7 +300,8 @@ struct rmnet_map_header *rmnet_map_add_map_header(struct sk_buff *skb,
 
 done:
 	map_header->pkt_len = htons(map_datalen + padding);
-	map_header->pad_len = padding & 0x3F;
+	/* This is a data packet, so the CMD bit is 0 */
+	map_header->flags = padding & MAP_PAD_LEN_MASK;
 
 	return map_header;
 }
diff --git a/include/linux/if_rmnet.h b/include/linux/if_rmnet.h
index 8c7845baf3837..a02f0a3df1d9a 100644
--- a/include/linux/if_rmnet.h
+++ b/include/linux/if_rmnet.h
@@ -6,21 +6,18 @@
 #define _LINUX_IF_RMNET_H_
 
 struct rmnet_map_header {
-#if defined(__LITTLE_ENDIAN_BITFIELD)
-	u8  pad_len:6;
-	u8  reserved_bit:1;
-	u8  cd_bit:1;
-#elif defined (__BIG_ENDIAN_BITFIELD)
-	u8  cd_bit:1;
-	u8  reserved_bit:1;
-	u8  pad_len:6;
-#else
-#error	"Please fix <asm/byteorder.h>"
-#endif
-	u8  mux_id;
-	__be16 pkt_len;
+	u8 flags;			/* MAP_CMD_FLAG, MAP_PAD_LEN_MASK */
+	u8 mux_id;
+	__be16 pkt_len;			/* Length of packet, including pad */
 }  __aligned(1);
 
+/* rmnet_map_header flags field:
+ *  PAD_LEN:	number of pad bytes following packet data
+ *  CMD:	1 = packet contains a MAP command; 0 = packet contains data
+ */
+#define MAP_PAD_LEN_MASK		GENMASK(5, 0)
+#define MAP_CMD_FLAG			BIT(7)
+
 struct rmnet_map_dl_csum_trailer {
 	u8  reserved1;
 #if defined(__LITTLE_ENDIAN_BITFIELD)
-- 
2.27.0

[PATCH net-next v4 5/6] net: qualcomm: rmnet: don't use C bit-fields in rmnet checksum trailer

[Alex Elder]

Replace the use of C bit-fields in the rmnet_map_dl_csum_trailer
structure with a single one-byte field, using constant field masks
to encode or get at embedded values.

Signed-off-by: Alex Elder <elder@linaro.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
---
v3: - Use BIT(x) and don't use u8_get_bits() for the checksum valid flag

 .../ethernet/qualcomm/rmnet/rmnet_map_data.c    |  2 +-
 include/linux/if_rmnet.h                        | 17 +++++++----------
 2 files changed, 8 insertions(+), 11 deletions(-)

diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
index 3c3307949db00..3df23365497c4 100644
--- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
+++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
@@ -365,7 +365,7 @@ int rmnet_map_checksum_downlink_packet(struct sk_buff *skb, u16 len)
 
 	csum_trailer = (struct rmnet_map_dl_csum_trailer *)(skb->data + len);
 
-	if (!csum_trailer->valid) {
+	if (!(csum_trailer->flags & MAP_CSUM_DL_VALID_FLAG)) {
 		priv->stats.csum_valid_unset++;
 		return -EINVAL;
 	}
diff --git a/include/linux/if_rmnet.h b/include/linux/if_rmnet.h
index a02f0a3df1d9a..941997df9e088 100644
--- a/include/linux/if_rmnet.h
+++ b/include/linux/if_rmnet.h
@@ -19,21 +19,18 @@ struct rmnet_map_header {
 #define MAP_CMD_FLAG			BIT(7)
 
 struct rmnet_map_dl_csum_trailer {
-	u8  reserved1;
-#if defined(__LITTLE_ENDIAN_BITFIELD)
-	u8  valid:1;
-	u8  reserved2:7;
-#elif defined (__BIG_ENDIAN_BITFIELD)
-	u8  reserved2:7;
-	u8  valid:1;
-#else
-#error	"Please fix <asm/byteorder.h>"
-#endif
+	u8 reserved1;
+	u8 flags;			/* MAP_CSUM_DL_VALID_FLAG */
 	__be16 csum_start_offset;
 	__be16 csum_length;
 	__be16 csum_value;
 } __aligned(1);
 
+/* rmnet_map_dl_csum_trailer flags field:
+ *  VALID:	1 = checksum and length valid; 0 = ignore them
+ */
+#define MAP_CSUM_DL_VALID_FLAG		BIT(0)
+
 struct rmnet_map_ul_csum_header {
 	__be16 csum_start_offset;
 #if defined(__LITTLE_ENDIAN_BITFIELD)
-- 
2.27.0

[PATCH net-next v4 6/6] net: qualcomm: rmnet: don't use C bit-fields in rmnet checksum header

[Alex Elder]

Replace the use of C bit-fields in the rmnet_map_ul_csum_header
structure with a single two-byte (big endian) structure member,
and use masks to encode or get values within it.  The content of
these fields can be accessed using simple bitwise AND and OR
operations on the (host byte order) value of the new structure
member.

Previously rmnet_map_ipv4_ul_csum_header() would update C bit-field
values in host byte order, then forcibly fix their byte order using
a combination of byte swap operations and types.

Instead, just compute the value that needs to go into the new
structure member and save it with a simple byte-order conversion.

Make similar simplifications in rmnet_map_ipv6_ul_csum_header().

Finally, in rmnet_map_checksum_uplink_packet() a set of assignments
zeroes every field in the upload checksum header.  Replace that with
a single memset() operation.

Signed-off-by: Alex Elder <elder@linaro.org>
---
v4: - Don't use u16_get_bits() to access the checksum field offset
v3: - Use BIT(x) and don't use u16_get_bits() for single-bit flags
v2: - Fixed to use u16_encode_bits() instead of be16_encode_bits().

 .../ethernet/qualcomm/rmnet/rmnet_map_data.c  | 34 ++++++-------------
 include/linux/if_rmnet.h                      | 21 ++++++------
 2 files changed, 21 insertions(+), 34 deletions(-)

diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
index 3df23365497c4..bdb6ab6dad83d 100644
--- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
+++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
@@ -197,23 +197,19 @@ rmnet_map_ipv4_ul_csum_header(void *iphdr,
 			      struct rmnet_map_ul_csum_header *ul_header,
 			      struct sk_buff *skb)
 {
-	__be16 *hdr = (__be16 *)ul_header;
 	struct iphdr *ip4h = iphdr;
 	u16 offset;
+	u16 val;
 
 	offset = skb_transport_header(skb) - (unsigned char *)iphdr;
 	ul_header->csum_start_offset = htons(offset);
 
-	ul_header->csum_insert_offset = skb->csum_offset;
-	ul_header->csum_enabled = 1;
+	val = MAP_CSUM_UL_ENABLED_FLAG;
 	if (ip4h->protocol == IPPROTO_UDP)
-		ul_header->udp_ind = 1;
-	else
-		ul_header->udp_ind = 0;
+		val |= MAP_CSUM_UL_UDP_FLAG;
+	val |= skb->csum_offset & MAP_CSUM_UL_OFFSET_MASK;
 
-	/* Changing remaining fields to network order */
-	hdr++;
-	*hdr = htons((__force u16)*hdr);
+	ul_header->csum_info = htons(val);
 
 	skb->ip_summed = CHECKSUM_NONE;
 
@@ -240,24 +236,19 @@ rmnet_map_ipv6_ul_csum_header(void *ip6hdr,
 			      struct rmnet_map_ul_csum_header *ul_header,
 			      struct sk_buff *skb)
 {
-	__be16 *hdr = (__be16 *)ul_header;
 	struct ipv6hdr *ip6h = ip6hdr;
 	u16 offset;
+	u16 val;
 
 	offset = skb_transport_header(skb) - (unsigned char *)ip6hdr;
 	ul_header->csum_start_offset = htons(offset);
 
-	ul_header->csum_insert_offset = skb->csum_offset;
-	ul_header->csum_enabled = 1;
-
+	val = MAP_CSUM_UL_ENABLED_FLAG;
 	if (ip6h->nexthdr == IPPROTO_UDP)
-		ul_header->udp_ind = 1;
-	else
-		ul_header->udp_ind = 0;
+		val |= MAP_CSUM_UL_UDP_FLAG;
+	val |= skb->csum_offset & MAP_CSUM_UL_OFFSET_MASK;
 
-	/* Changing remaining fields to network order */
-	hdr++;
-	*hdr = htons((__force u16)*hdr);
+	ul_header->csum_info = htons(val);
 
 	skb->ip_summed = CHECKSUM_NONE;
 
@@ -425,10 +416,7 @@ void rmnet_map_checksum_uplink_packet(struct sk_buff *skb,
 	}
 
 sw_csum:
-	ul_header->csum_start_offset = 0;
-	ul_header->csum_insert_offset = 0;
-	ul_header->csum_enabled = 0;
-	ul_header->udp_ind = 0;
+	memset(ul_header, 0, sizeof(*ul_header));
 
 	priv->stats.csum_sw++;
 }
diff --git a/include/linux/if_rmnet.h b/include/linux/if_rmnet.h
index 941997df9e088..4efb537f57f31 100644
--- a/include/linux/if_rmnet.h
+++ b/include/linux/if_rmnet.h
@@ -33,17 +33,16 @@ struct rmnet_map_dl_csum_trailer {
 
 struct rmnet_map_ul_csum_header {
 	__be16 csum_start_offset;
-#if defined(__LITTLE_ENDIAN_BITFIELD)
-	u16 csum_insert_offset:14;
-	u16 udp_ind:1;
-	u16 csum_enabled:1;
-#elif defined (__BIG_ENDIAN_BITFIELD)
-	u16 csum_enabled:1;
-	u16 udp_ind:1;
-	u16 csum_insert_offset:14;
-#else
-#error	"Please fix <asm/byteorder.h>"
-#endif
+	__be16 csum_info;		/* MAP_CSUM_UL_* */
 } __aligned(1);
 
+/* csum_info field:
+ *  OFFSET:	where (offset in bytes) to insert computed checksum
+ *  UDP:	1 = UDP checksum (zero checkum means no checksum)
+ *  ENABLED:	1 = checksum computation requested
+ */
+#define MAP_CSUM_UL_OFFSET_MASK		GENMASK(13, 0)
+#define MAP_CSUM_UL_UDP_FLAG		BIT(14)
+#define MAP_CSUM_UL_ENABLED_FLAG	BIT(15)
+
 #endif /* !(_LINUX_IF_RMNET_H_) */
-- 
2.27.0

Re: [PATCH net-next v4 0/6] net: qualcomm: rmnet: stop using C bit-fields

[Alexander Duyck]

On Mon, Mar 15, 2021 at 6:36 AM Alex Elder <elder@linaro.org> wrote:
>
> The main reason for version 4 of this series is that a bug was
> introduced in version 3, and that is fixed.
>
> But a nice note from Vladimir Oltean got me thinking about the
> necessity of using accessors defined in <linux/bitfield.h>, and I
> concluded there was no need.  So this version simplifies things
> further, using bitwise AND and OR operators (rather than, e.g.,
> u8_get_bits()) to access all values encoded in bit fields.
>
> This version has been tested using IPv4 with checksum offload
> enabled and disabled.  Traffic over the link included ICMP (ping),
> UDP (iperf), and TCP (wget).
>
> Version 3 of this series used BIT() rather than GENMASK() to define
> single-bit masks, and bitwise AND operators to access them.
>
> Version 2 fixed bugs in the way the value written into the header
> was computed in version 1.
>
> The series was first posted here:
>   https://lore.kernel.org/netdev/20210304223431.15045-1-elder@linaro.org/
>
>                                         -Alex
>
> Alex Elder (6):
>   net: qualcomm: rmnet: mark trailer field endianness
>   net: qualcomm: rmnet: simplify some byte order logic
>   net: qualcomm: rmnet: kill RMNET_MAP_GET_*() accessor macros
>   net: qualcomm: rmnet: use masks instead of C bit-fields
>   net: qualcomm: rmnet: don't use C bit-fields in rmnet checksum trailer
>   net: qualcomm: rmnet: don't use C bit-fields in rmnet checksum header
>
>  .../ethernet/qualcomm/rmnet/rmnet_handlers.c  | 10 +--
>  .../net/ethernet/qualcomm/rmnet/rmnet_map.h   | 12 ----
>  .../qualcomm/rmnet/rmnet_map_command.c        | 11 +++-
>  .../ethernet/qualcomm/rmnet/rmnet_map_data.c  | 60 ++++++++---------
>  include/linux/if_rmnet.h                      | 65 +++++++++----------
>  5 files changed, 69 insertions(+), 89 deletions(-)
>

Other than the minor nit I pointed out in patch 2 the set looks good to me.

Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>